BT premium phone calls/costs problems

The filters etc are the original ones from BT and they have not changed as far as I know.

Just added up all the costs for that one number, since May 2012 its cost a whopping £480.09 !!!

I suspect it could be more, but the online BT account only dates back so far...

I will have a look around the house. I am thinking its a crossed line/error.

Just been speaking with my dad and he also mentioned that the telegraph pole and cables outside, which runs the line to the other 3 cottages next door to there house were replaced sometime last year....